Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
  • C22C21/02—Alloys based on aluminium with silicon as the next major constituent
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
  • C22F1/043—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon of alloys with silicon as the next major constituent

Definitions

• the present invention describes a method of fabricating an aluminum foil suitable for application in fins used in heat exchangers, particularly for condenser and evaporator coils.
• Aluminum foils are popularly used in heat exchangers because aluminum has very high thermal conductivity. These fins are typically fitted over copper tubes and mechanically assembled. As the size of the air conditioner units increases, the fins become longer, and it is important that they have sufficient strength so that they can be lifted without bending. Low strength can also result in handling damage when the coils are bent to form a unit.
• One way to improve the rigidity of the coil is to increase the gauge of the aluminum foil. Since this alternative is costly, and adds weight, air conditioner manufacturers prefer to use stronger foil.
• alloy AA 1100 The most popular alloy used in this application is the alloy AA 1100. It has the composition shown in Table I below:
• this alloy When fully annealed, this alloy has very low strength. For example, typical yield strength could be between 20.7–41.4 MPa (3–6 ksi), and ultimate tensile strength (UTS) could be between 96.5–110.3 MPa (14–16 ksi).
• This alloy is highly formable, with elongation generally exceeding 24% and Olsen values above 0.25 in. (6 mm). If the formability is inadequate, the collars formed in this sheet through which the copper tubes are passed can crack in the reflare or in the body of the collar itself. These cracks are undesirable because the copper tubes, after passing through the fins, are expanded to form a good joint between the collar and the tube. If the collar is cracked, heat transfer between the fin and the tube deteriorates. “0” temper, AA 1100 sheet forms excellent collars and is popularly used in this application. A problem arises when higher strength is desired in applications such as long fins.
• AA 1100 alloy formed by direct casting or DC method hot rolled and then cold rolled to the final gauge of 0.1–0.13 mm (0.004–0.005 in), can be partially annealed.
• the partial anneal step involves heating the cold rolled sheet at temperatures between 240–270° C. During this time, the strength of the cold rolled sheet decreases and its formability increases. The cold rolling destroys the aluminum structure completely.
• the first step involves recovery and the second step involves recrystallization. In a typical anneal, the step of recovery involves a gradual reduction in strength while recrystallization involves precipitous decline in strength.
• Table II The typical desired mechanical properties of a partially annealed sheet are shown in Table II below:
• the partially annealed material has a structure that is fully recovered and has started forming some initial grains (incipient recrystallization). These grains are small, typically less than 25 micron in diameter. This material performs extremely well in fin application with collar cracks generally below 5%.
• DC casting method is expensive. In recent years, there has been a trend to go to continuous casting, using belt casters, roll casters, or other similar equipment.
• Continuous casters produce an “as-cast” strip that is less than 30 mm in thickness (more generally less than 25 mm in thickness).
• Roll casters generally produce a strip of 6 mm or less that can be directly cold rolled.
• Belt casters produce strip that can be either directly cold rolled or may be used in conjunction with an in-line rolling mill that reduces the thickness of the as cast slab, after it is solidified but before it cools, to a thickness suitable for cold rolling.
• the hot rolling step in DC cast material is preceded by a preheat (homogenization) at around 500° C.
• U.S. Pat. No. 5,466,312 discusses a method of making an aluminum foil which comprises providing a molten aluminum-based alloy consisting essentially of about 0.08 to 0.20 weight percent silicon, about 0.24 to 0.50 weight percent iron, and about 0.21 to 0.30 weight percent copper, with the balance being aluminum and inevitable impurities.
• the aluminum alloy composition is continuously cast to form a coiled cast strip.
• the coiled cast strip is homogenized, cold rolled, and followed by a final recrystallizing annealing step of 450–650° F. This temperature range creates recrystallization in the foil.
• U.S. Pat. No. 5,554,234 proposes high strength aluminum alloy suitable for use in the manufacture of a fin.
• the aluminum alloy contains at most 0.1% by weight of silicon, 0.10 to 1.0% by weight of iron, 0.1 to 0.50% by weight of manganese, 0.01 to 0.15% by weight of titanium, with the balance being aluminum and unavoidable impurities.
• the patent also discusses a method of manufacturing a high strength aluminum alloy suitable for use in the manufacture of a fin, which comprises the step of heating an aluminum alloy ingot to 430–580° C., hot rolling the ingot to obtain a plate material, and applying a homogenizing annealing treatment at 250–350° C. for the stated purpose of causing intermetallic compounds to be distributed within the metal texture of the alloy.
• U.S. Pat. No. 4,737,198 discloses a method of casting an alloy having components in the composition range of about 0.5–1.2% iron, 0.7–1.3% manganese, and 0–0.5% silicon by weight, homogenizing the cast alloy at temperatures below about 1100° F., preferably below about 1050° F. to control the microstructure, and cold rolling to a final gauge. The cold rolled alloy is then partially annealed to attain desired levels of strength and formability.
• Japanese Patent No. 5-51710 proposes an aluminum foil annealed at 150–250° C. in a hot air furnace which carries the foil along on a hot air cushion at a temperature of 350–450° C.
• Japanese Patent No. 6-93397 discusses an aluminum alloy for making a foil and a treatment method to improve the properties of the foil, including cold rolling, heat treatment up to 400 C., and then process annealing at 250–450 C., followed by further cold rolling.
• the present invention provides a method for making an aluminum alloy foil for fins used in heat exchangers.
• the alloy may be an AA 1100 type aluminum alloy, such as an aluminum alloy containing about 0.27% to about 0.55% by weight of iron and about 0.06% to about 0.55% by weight of silicon.
• the alloy also preferably contains about 0.05% to about 0.20% by weight copper.
• This alloy in molten form is continuously cast into an aluminum alloy strip, which continuously cast strip is cold rolled to a final gauge of about 0.076 mm to about 0.152 mm.
• the cold rolled strip is subjected to a partial annealing treatment at a temperature below about 260° C., with a maximum overheat of about 10° C. In this manner, the annealing of the aluminum alloy foil takes place with substantially no recrystallization.
• the invention provides a strong yet formable improved aluminum alloy foil suitable for use in making fins for heat exchangers, including condensers and evaporators used in air conditioning equipment.
• CC and DC cast material cannot be explained in terms of the alloy composition. For instance, aluminum alloys of various compositions including high and low Fe (0.27–0.55%), high and low silicon (0.06–0.55%), and changes in copper content (0.00–0.12%) were tried but the result was always the same.
• the CC cast material was less formable than the DC cast material. For example, the elongation of DC cast material when the yield strength is 96.5 MPa is around 22%. The corresponding yield strength at equivalent elongation for the CC cast material was around 48.3–62.1 MPa.
• CC cast and DC cast material can be traced to the difference in the microstructure of the two partially annealed materials.
• the DC cast material forms small grains but the CC cast material forms large grains. This may be due to the fact that fewer recrystallization sites are available in CC cast material due to the presence of these large grains rather than the bulk formability.
• collar cracks were caused by inadequate elongation or Olsen values. This was only partially true.
• the partially recrystallized material did not contain more than 5% of recrystallized grains, preferably not more than 2% of recrystallized grains, collar cracks did not form even when the elongation was only between 16–18%.
• the presence of large grains in CC material could not only be correlated to the anneal temperature but also to the overheat provided in the furnace.
• Heat head, or overheat is the difference between the metal and air or gas temperatures in the furnace.
• the air or gas temperature is measured directly by a thermocouple near the heat source and in the air flow in furnace and the metal temperature is generally measured by a thermocouple embedded within the coil in the furnace.
• the anneal temperature should not exceed 260° C., and preferably should be between 245–255° C.
• the overheat should not exceed 10° C., preferably should be less than 7° C. Under these circumstances, no recrystallization takes place.
• the anneal time is provided to finish recovery of the material.
• the low overheat imposed in the present method ensures the greatest possible uniformity of temperature during the anneal process and consequently the formation of even small amounts of recrystallized grains is prevented whilst operating at the highest possible temperature for recovery.
• CC cast material gives a microstructure that is essentially recovered and has very few, if any, recrystallized grains.
• Table III The typical properties of such a material are shown in Table III below:
• this material performs extremely well in fin applications.
• the present invention includes continuously casting a Cu—Fe—Si—Al alloy and fabricating the alloy to a light gauge sheet or foil, e.g., sheet having approximately 0.076–0.152 mm thickness, followed by controlled partial annealing to achieve combinations of strength and formability not achieved by conventional techniques.
• the partial anneal is preferably carried out a batch anneal with the cold rolled sheet in coil form.
• the silicon range of 0.3–0.5 wt % preferably 0.36–0.44 wt % and iron range of 0.3–0.5 wt % preferably 0.39–0.47% are chosen so that during the continuous casting process a single intermetallic species (alpha phase) is formed. Since the material does not undergo any subsequent homogenization process, this prevents the formation of surface rolling defects (“smut”) during the cold rolling process.
• smut surface rolling defects
• Copper in the range given adds strength to the final product without causing excessive work hardening during the foil rolling stage.
• the specified alloy is cast using a belt caster and in-line rolling mill to 1.7 mm gauge.
• the alloy is then cold rolled to the final product gauge.
• the final product gauge is in the range of about 0.076–0.152 mm. Partial annealing is then employed to optimize strength and formability.
• An example of the combined strength and formability that can be achieved for an annealing temperature of 250° C. is shown in Table V below.
• the process of the present invention has been found to develop a fine grained, high strength fin stock alloy with good formability.
• the alloy is particularly useful in producing light gauge sheet or foil for fin stock.
• the process of the present invention does not contain a hot rolling step preceded by a preheat at around 500° C.
• Step 1 UTS YS Elong Olsen over Coil Temp ° C. Time Temp ° C. Time MPa MPa % mm DC % 1 235 2 258 6 119.8 92.8 18.0 6.0 14 2 235 2 262 6 110.3 75.2 22.0 6.1 41.6 3 235 2 262 6.5 106.1 63.4 20.5 6.4 52 4 235 2 262 6.5 101.3 52.4 21 7.0 58
• the reflare cracks generally increased with increasing elongation and decreasing yield strength.
• the structure revealed presence of large grains that were partially recrystallized.
• the DC structure showed only very small grains, if any. The onset of large grains was probably caused by the high heat head which was maintained in the furnace and which caused a part of the coil to reach temperatures significantly higher than the target resulting in grain growth.

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• Chemical & Material Sciences (AREA)
• Mechanical Engineering (AREA)
• Organic Chemistry (AREA)
• Metallurgy (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Crystallography & Structural Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Continuous Casting (AREA)
• Metal Rolling (AREA)
• Diaphragms For Electromechanical Transducers (AREA)
• Chemical Treatment Of Metals (AREA)

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• 2001
  • 2001-07-04 ES ES01951260T patent/ES2225577T3/es not_active Expired - Lifetime
  • 2001-07-04 CA CA002411128A patent/CA2411128C/en not_active Expired - Lifetime
  • 2001-07-04 US US10/297,941 patent/US7172664B2/en not_active Expired - Lifetime
  • 2001-07-04 DE DE60106445T patent/DE60106445T2/de not_active Expired - Fee Related
  • 2001-07-04 JP JP2002509543A patent/JP2004502038A/ja active Pending
  • 2001-07-04 AT AT01951260T patent/ATE279545T1/de not_active IP Right Cessation
  • 2001-07-04 AU AU2001272244A patent/AU2001272244A1/en not_active Abandoned
  • 2001-07-04 KR KR1020027017628A patent/KR100790202B1/ko not_active IP Right Cessation
  • 2001-07-04 EP EP01951260A patent/EP1297194B1/en not_active Expired - Lifetime
  • 2001-07-04 WO PCT/CA2001/000965 patent/WO2002004690A2/en active IP Right Grant
  • 2001-07-05 MY MYPI20013205A patent/MY128402A/en unknown

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